In a biometric authentication system, information indicating characteristics of a body (which will be called “characteristic information” below) is previously enrolled as biometric information in the system and a similarity between the enrolled biometric information and biometric information obtained on authentication is determined thereby to execute personal authentication. In principle, the biometric information obtained on the enrollment will not strictly match with the biometric information obtained on the authentication, and when it is determined that the similarity is low, even a person enrolled in the system may fail the authentication. A threshold for determining the similarity is reduced and thus a possibility that the person fails the authentication (false rejection rate) decreases, but in this case, a possibility that a stranger is erroneously determined as authenticated (false acceptance rate) increases. Typically, the false rejection rate and the false acceptance rate are in a contradictory relationship, but there is known a method in which multiple types of biometric information are used to execute personal authentication, thereby simultaneously reducing both the rates and improving an authentication precision.
There is a technique in which a palm vein pattern is used as biometric information. The technique is such that characteristic information of a user's palm vein pattern is enrolled as biometric information in a system and a similarity between the input vein pattern on authentication and the characteristic information is determined. The techniques using a palm vein pattern includes the following conventional techniques. For example, there is a conventional technique in which both a device into which finger images are to be input and a device into which a palm image is to be input are integrally arranged. There is a conventional technique in which a passcode and a palm print are used for authentication. There is a conventional technique in which an image of wrinkles of a finger's joint is generated as a high-contrast image. Further, there is a conventional technique in which a target position for obtaining one type of biometric information is corrected based on a target position for obtaining another type of biometric information. Furthermore, there is a conventional technique in which the amount of finger tips' positional deviation occurring between the fingerprint enrollment and the fingerprint verification is calculated to execute authentication.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2006-331239
Patent Literature 2: Japanese Laid-open Patent Publication No. 07-114640
Patent Literature 3: Japanese Laid-open Patent Publication No. 2000-194828
Patent Literature 4: Japanese Laid-open Patent Publication No. 2006-277341
Patent Literature 5: Japanese Laid-open Patent Publication No. 2008-198083
However, it is preferable that the entire palm is shot for an image of the palm vein pattern, but only the left half or right half of the palm can be shot depending on the shape of a guide on which the palm is to be placed or the position at which the palm is placed. For example, in the conventional technique in which a device into which finger images are to be input and a device into which a palm image is to be input are integrally arranged, the position on which the palm is to be placed is restricted and it is difficult to shot the entire palm. In the conventional technique in which one position of a target is corrected based on another position of the target whose biometric information is to be obtained, a schematic size of a body part or a contour of a fingerprint pattern is used. However, the size of a body part or the shape of the fingerprint pattern is largely different between persons, and thus the position is difficult to accurately correct. Further, in the conventional technique in which the amount of finger tips' positional deviation occurring between the fingerprint enrollment and the fingerprint verification is calculated to execute authentication, one item of biometric information is authenticated for detecting the amount of positional deviation of another item of biometric information to be obtained. Therefore, when the conventional technique is applied to a one-to-many authentication system, for example, so many items of biometric information have to be verified, which is complicated. There is a technique in which part of a palm is rotated and shot. However, a complicated processing is needed for stereoscopically recognizing the palm, and it can take much time to take the image.
As stated above, when the degree of freedom of how to place a palm is increased, it takes much time to take an image, and the degree of freedom of how to place a palm is restricted for performing an image-taking processing in a short time, and thus a proper image cannot be obtained.